While bass playback in a speaker system is dependent on the cabinet, there are various types of cabinets each reproducing distinctive sound based on the size, shape and system of the acoustic device required. In one of the cabinets that take into consideration sound playback, a bass reflex type speaker is used that actively employs sound wave from the rear surface of the speaker. To enhance bass playback capability, the bass reflex type speaker, also referred to as phase inverted type, is designed to upgrade the bass characteristic radiated from the speaker's vibrating surface to its entire surface by providing openings and a duct in a baffle plate provided with the speaker, by inverting the phase of sound coming out from the rear surface of the speaker diaphragm and by radiating the sound externally from the openings via the duct. By using such a phase inverted type cabinet, it is possible to flatly reproduce sound down to a lower level of bass than the speaker unit is capable of reproducing.
FIG. 1 is a perspective view showing a configuration example of a conventional speaker apparatus, with 40 representing the speaker apparatus and the speaker apparatus having a duct 41. As the aforementioned bass reflex type speaker apparatus, an apparatus is disclosed as shown in FIG. 1 that is designed to upgrade the bass characteristic by extracting, in general, radiation from the duct to the listener's side, that is, to the speaker's opening surface side and using the bass reflex effect thereof (see, e.g., Patent Documents 1 and 2).
As disclosed in the embodiment of Patent Document 1, there exists another apparatus that adjusts the bass characteristic by projecting a substantially U-shaped duct on the rear surface of the box, fastening the duct diagonally along the rear surface wall of the box and reinforcing the wall member.
Further, as a conventional example of providing a speaker integral with a woofer box within the main body of a CRT television set, there is proposed an apparatus that releases sound by extending a woofer box output port externally and downward of the box and releases sound toward the front surface after causing sound wave to be reflected by the external bottom surface (see, e.g., Patent Document 3).
The aforementioned prior arts all relate to apparatuses that are either a speaker box used alone or a speaker designed to upgrade bass by using a space deep to a certain extent such as CRT television.
With a growing number of display devices available recently using thin displays such as liquid crystal, PDP (Plasma Display) and EL televisions, there are demands for mounting a woofer speaker—either speaker integrated type or deep to the same extent as the depth of the display device for design purposes—within the main bodies of these thin display devices and reproducing attractive bass. As a speaker for use in such thin display devices, speaker cabinet is required to be compact and lightweight to the extent possible and thin in shape. However, if it is desired to reproduce powerful bass while retaining the distinctive bass effect as bass reflex type speaker, the cabinet is required to be of a fixed volume or more. In particular, the depth from a speaker opening portion to a rear surface cabinet should be a fixed size or more.
As a solution to the aforementioned problem, while it is possible to form a speaker portion, for example, by using the entire rear surface of the flat display as widely as possible, the problem of widening of required two-dimensional area remains unsolved. Further, as described earlier, the bass reflex effect is often used by extracting the external opening (port) provided at one end of the duct on the same surface as the speaker opening surface or on the rear surface in many conventional bass reflex type speaker boxes. In an example of extending the opening at one end of the duct downward into the speaker box, the purpose of the opening is to suck inner air, and these speaker boxes are used in an environment where the inner space thereof can be widely used to a certain extent.
Recent years have seen demands for mounting, within the main body of a thin display device as thick as about 10 to 20 cm such as liquid crystal television, a woofer speaker—either speaker integrated type or deep to the same extent as the depth of the display device's main body as described above, thus stressing the bass effect. In this case, if sound playback is attempted by arranging a woofer at the center and mid/treble stereo speakers on the left and right near there in the thin display device, with the woofer close to the stereo speakers on the right and left, sound component in the mid/treble range other than bass range leaks out from the center woofer, deteriorating the stereo feeling. When a woofer speaker is used in such an arrangement, it is possible to enjoy sufficient bass without necessarily releasing the bass reflex duct on the same side as the opening side of the speaker unit.
When a speaker unit-integrated dome-shaped speaker such as the aforementioned speaker is mounted in a conventional thin television receiver, the speaker unit is fixed, using mounting holes (generally two to four holes) provided on the outer perimeter thereof and with screws or others, to the mounting bosses provided on the front or back cabinet side of the television receiver or to mounting portions on the front cabinet's main body, in order to prevent jitter of the television screen due to vibrations of the speaker's main body.
As a conventional speaker box mounting structure, means are disclosed for pressing and fixing a speaker unit with fitting ribs provided on the dome's main body and the back cabinet of the television receiver (see, e.g., Patent Document 4).
As means for fixing a speaker box within a television receiver, means are disclosed for mounting a pair of left and right speaker boxes to the front cabinet of a television receiver (see, e.g., Patent Document 5).
Incidentally, if an attempt is made to reproduce powerful bass by mounting a woofer speaker-integrated thin speaker box within the enclosure of a television receiver having a thin display device as described above, sound pressure, radiated to the rear surface side of the speaker box, is high in addition to bass pressure radiated to the speaker unit's opening portion (front surface side) of the speaker box during woofer speaker playback, unlike mid/treble playback. Therefore, if the woofer speaker box is fixed only to the front cabinet side of the television receiver's main body using a plurality of mounting portions provided on the outer perimeter of the woofer speaker box, vibrations of the speaker box conduct only to the front cabinet side of the television receiver's main body through the plurality of mounting portions, thus resulting in jitter of the screen itself or vibrations of the receiver's entire enclosure.
If, in order to dissipate the vibrations through distributed conduction by integrally using the front and back cabinets of the television receiver's main body, all the plurality of mounting holes provided on the outer perimeter of the woofer speaker box are pressed, tightened together and fixed using both the front and back cabinets of the receiver's main body, vibrations of the speaker box's main body resulting from woofer sound pressure conduct between both cabinets through all of the plurality of mounting and fixing portions in a plurality of paths, affecting not only the display unit of the television receiver's main body but also other portions as a whole and resulting in jitter of the screen itself and vibrations of the receiver's entire enclosure as described earlier.
In particular, if a woofer box is incorporated in the enclosure of a television receiver using a thin display device, because the enclosure is vertically or horizontally thin, and combined with other restrictions such as incapability of taking large space along the depth of the enclosure, the space for sound pressure radiated from the rear surface of the woofer speaker unit, in particular, is narrow, making the screen and the receiver's main body more prone to jitter and vibration than conventional CRT type television receiver and making it impossible to increase the woofer output beyond a fixed level.
In light of the above, it is an object of the present invention to provide a speaker apparatus that can be integrated with the main body of a thin display device and that can be made more compact and thinner to about the same extent as the depth of the thin display device's main body. It is another object of the present invention to provide, when playback is performed with a woofer speaker and mid/treble stereo speakers arranged side by side on the same surface of a thin display device, a bass reflex type speaker apparatus that allows sensitivity improvement in bass range by sufficiently attenuating mid/treble sound component radiated from the woofer speaker.
It is still another object of the present invention to provide a speaker apparatus mounting structure and method capable of reproducing a sufficient level of bass and effectively suppressing vibrations of the display unit and vibrations of the entire enclosure even if the apparatus is mounted and fixed within the enclosure of a thin display device.
Patent Document 1: Japanese Laid-Open Patent Publication No. H06-217385
Patent Document 2: Japanese Laid-Open Patent Publication No. H04-114598
Patent Document 3: Japanese Laid-Open Patent Publication No. 2001-145186
Patent Document 4: Japanese Laid-Open Patent Publication No. H09-65251
Patent Document 5: Japanese Laid-Open Patent Publication No. H08-336194